Novel modulators of melanocortin receptors

ABSTRACT

Modulators of melanocortin receptors (MCR) are provided herein. An MC5R peptide ligand is represented by to Formula 1: 
       R 1 -Nle 4 - c [Xaa 5 -Yaa 6 -(NMe)D-Nal(2′) 7 -Arg 8 -Trp 9 -(NMe)Zaa 10 ]-R 2 .
 
     R 1  can be an acetyl, a glycosylated amino acid, —CO—(CH 2 ) n —CH 3 , or −CO—(CH 2 ) n CF 3  with n ranging from 1 to 6. R 2  can be an —CONH 2 , —COOH, or —CH 2 OH. Xaa, Yaa, and Zaa can each be a natural amino acid or an unnatural amino acid.

CROSS REFERENCE

This application is a non-provisional and claims benefit of U.S. Provisional Patent Application No. 62/242,874, filed Oct. 16, 2015, the specification(s) of which is/are incorporated herein in their entirety by reference.

This application is a continuation-in-part and claims benefit of U.S. Patent Application No. PCT/US15/35180, filed Jun. 10, 2015, which claims benefit of U.S. Provisional Patent Application No. 62/017,137, filed Jun. 25, 2014, and U.S. patent application Ser. No. 14/300,991, filed Jun. 10, 2014, the specification(s) of which is/are incorporated herein in their entirety by reference.

FIELD OF THE INVENTION

The present invention relates to modulators of melanocortin receptors (MCR), in particular, to an N-methylated variation of a cyclic peptide and analogues thereof that are modulators for MC5R.

BACKGROUND OF THE INVENTION

The melanocortin system remains a challenging target for rational peptide and peptidomimetic design as the 3D-topographical requirements for specific melanocortin receptor subtype recognition have not been fully elucidated. Nevertheless, the numerous multifaceted physiological functions of the five known subtypes of human melanocortin receptors (hMC1-5R) continue to provide a strong stimulus for further development of potent and selective melanocortin agonists and antagonists.

On the other hand, development of selective ligands to melanocortin system bears intrinsic challenges due to conserved amino acid sequences and their structural similarity contained in the 7 transmembrane GPCR fold. Unlike other protein targets, hMCRs, known to be the smallest GPCRs have separate natural agonist and antagonist molecules for functional regulation. This aspect of hMCRs imposes a second dimension on melanocortin ligands for achieving selectivity not only to receptor subtype but also between the required agonistic and antagonistic properties. Designing such molecules which possess both functional selectivity and hMCR subtype selectivity from a four residue hMCR recognition sequence His-Phe-Arg-Trp is very demanding and necessitates to experiment with every possible molecule designing tool in peptide chemistry.

Great efforts have been made in the last decade to develop selective melanotropin peptides by following various general approaches. Application of such strategies has resulted in the development of cyclic peptides, such as Ac-Nle⁴-c[Asp⁵, D-Nal (2′)⁷, Lys¹⁰]α-MSH(4-10)-NH₂ (SHU9119). Although lacking exclusive receptor subtype selectivity, SHU9119 has been extensively used in understanding the combined functional aspects of hMCRs. A proper insight into the structure driven responses of melanocortin subtypes requires a systematic perturbation of ligand conformation. To accomplish this, the present invention is considered to modulate the peptide conformation and the functional side chain disposition of SHU9119 peptide by N-methylation of the backbone amide NHs.

Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.

SUMMARY OF THE INVENTION

Melanocortin receptors, MC1-5R are a family of five receptor compounds of the melanocortin receptor system. Prior to the invention, it has been difficult to target the receptors independently of one another. The key difference between the present invention and similar compounds is that the present invention is specific to individual types of melanocortin receptors, specifically to MC5R. An N-methylated form of SHU9119 and analogues thereof can antagonize MC5R. This could potentially reduce the amount of side effects incurred by the treatments involving the present invention.

According to one embodiment, the present invention features a melanocortin 5 receptor (MC5R) peptide ligand according to Formula 1:

R₁-Nle⁴-c[Xaa⁵-Yaa⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Zaa¹⁰]-R₂.

In some embodiments, R₁ may be an acetyl, —CO—(CH₂)_(n)CH₃, —CO—(CH₂)_(n)CF₃, or a glycosylated amino acid. Preferably, “n” can range from 1 to 6. In other embodiments, R₂ may be an —CONH₂, —COOH, or —CH₂OH. In one embodiment, Xaa, Yaa, and Zaa may each be a natural amino acid or an unnatural amino acid. The MC5R peptide ligand may be a cyclic peptide formed by the bridging of Xaa to Zaa via a carba, lactam, disulfide, thioether, or succinic linker. In another embodiment, the MC5R peptide ligand has a 23 to 27-membered ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of SHU 9119. The two arrows indicate the sites of N-methylation of the backbone NHs to form one embodiment of a MC5R modulator.

FIG. 2 shows a structure of an exemplary MC5R peptide ligand, PEPTIDE 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

Before the present compounds, compositions, articles, devices, and/or methods are disclosed and described, it is to be understood that this invention is not limited to specific synthetic methods or to specific compositions, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

Following is a list of abbreviations referred to herein:

-   Abu 2-aminobutyric acid -   Acpc 1-aminocyclopropane carboxylic acid -   Aic 2-aminoindane-2-carboxylic acid -   Che 1-amino-1-cyclohexane carboxylic acid -   Cpe 1-amino-1-cyclopentane carboxylic acid -   Dab diaminobutyric acid -   Ioc indoline-2-carboxyic acid -   Oic octahydroindole-2-carboxylic acid -   Orn ornithine -   Tic tetrahydro-isoquinoline-3-carboxylic Acid

As used herein, the term “natural amino acids” refers to the twenty amino acids that are found in nature, i.e. occur naturally. The natural amino acids are as follows: alanine, arginine, glycine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, serine, threonine, histidine, lysine, methionine, proline, valine, isoleucine, leucine, tyrosine, tryptophan, and phenylalanine. This application adheres to the IUPAC rules of standard abbreviations for amino acids.

As used herein, the term “unnatural amino acids” refers to amino acids that are not naturally encoded or found in the genetic code of any organisms. Typically, the unnatural amino acids are different from the twenty naturally occurring amino acids in their side chain functionality.

As defined herein, the term “antagonist” refers to compound that diminishes a response. The antagonist binds to the same site as the endogenous compound and diminishes or blocks the signal generated by the endogenous agent.

As defined herein, the term “N-methylation” refers to a form of alkylation wherein a methyl group, CH₃, replaces the hydrogen atom of the NH moiety in the backbone amide NHs of peptides.

As used herein, the term “NMe” preceding any three-letter abbreviation for an amino acid, i.e. (NMe)Lys, denotes the N-methylated form of the amino acid. As used herein, the term “Nle” refers to a Norleucine. As used herein, the term “c” or “cyclo” means cyclic, i.e. a cyclic peptide.

As used herein, the term “glycosylated” is defined as a saccharide (or sugar) covalently attached, i.e. linked, to an amino acid. Specifically, the saccharide is linked to the side-chain of the amino acid.

According to one embodiment, the present invention features a melanocortin 5 receptor (MC5R) peptide ligand according to Formula 1:

R₁-Nle⁴-c[Xaa⁵-Yaa⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Zaa¹⁰]-R₂.

According to a preferred embodiment, the MC5R peptide ligand is an antagonist of MC5R. Alternatively, other embodiments of the MC5R peptide ligand may be agonists of MC5R.

N-Terminal Modification

In some embodiments, R₁ may be a glycosylated amino acid. In one aspect, the glycosylated amino acid may comprise a saccharide O-linked to a natural amino acid. For instance, the saccharide is attached to the hydroxyl group of the side-chain of the amino acid, such as Ser, Thr, or Tyr. In another aspect, the glycosylated amino acid may comprise a saccharide N-linked to a natural amino. For example, the saccharide is attached to the amine group of the side-chain of the amino acid, such as Asn or Lys. The saccharide may be a monosaccharide, a disaccharide, or an oligosaccharide. Examples of saccharides include, but are not limited to, glucose, fructose, and lactose.

In other embodiments, acetylation of the N-terminal results in R₁ being an acetyl. In further embodiment, R₁ may be —CO—(CH₂)_(n)CH₃ or —CO—(CH₂)_(n)CF₃. Preferably, “n” can range from 1 to 6.

Without wishing to limit the invention to a particular theory or mechanism, N-terminal modifications may play a role in stability, protein folding, cellular attachment, and function modulation of the MC5R peptide ligand.

C-Terminal Modification

In further embodiments, R₂ may be an —CONH₂, —COOH, or —CH₂OH. Without wishing to limit the invention to a particular theory or mechanism, C-terminal modifications, such as amidation, can enhance the biological activity of the peptide ligand, increase the ligand's stability, efficacy, and ability to enter cells, as well as increase its ability to resist enzymatic degradation.

Amino Acid Modifications

In one embodiment, Xaa may be a natural amino acid or an unnatural amino acid. For example, Xaa may be the natural amino acid Asp or Glu, or the unnatural amino acid Abu.

In another embodiment, Yaa may be a natural amino acid such as His or Pro, or an unnatural amino acid such as Oic, Ioc, Tic, Cpe, Che, Aic, and Acpc. Without wishing to limit the invention to a particular theory or mechanism, the Yaa modification can provide for a stable β turn-like structure and improved potency of the MC5R peptide ligand.

In a further embodiment, Zaa may be a natural amino acid such as Lys, or an unnatural amino acid such as Orn, and Dab.

In one alternate embodiment, a side-chain of the amino acid in the cyclic peptide may be halogenated. For example, if Yaa is His, then the side-chain of His may be halogenated. As another example, the side-chain of (NMe)D-Nal(2′) or Trp in the cyclic peptide may be para-, meta-, or ortho-halogenated or di-halogenated. In another alternate embodiment, a side-chain of the amino acid may be glycosylated. For example, the side-chain of Lys in the cyclic peptide may be glycosylated.

It is understood that the aforementioned examples of R₁, R₂, Xaa, Yaa, and Zaa are non-limiting. For instance, Xaa, Yaa, and Zaa can be any natural amino acid or unnatural amino acid. Preferably, R₁, R₂, Xaa, Yaa, and Zaa are each selected to produce a specific MC5R peptide ligand having desired properties.

Without wishing to limit the present invention to a particular theory or mechanism, N-methylation of the backbone NHs as indicated in FIG. 1 can provide for an increase in blood-brain barrier penetration, selectivity, and stability of the MC5R peptide ligand. A non-limiting example of an MC5R peptide ligand resulting from N-methylation of sites indicated in FIG. 1 is the following peptide:

Ac-Nle⁴-c[Asp⁵-His⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Lys¹⁰]-NH₂  (PEPTIDE 9)

Shown in FIG. 2 is PEPTIDE 9, in which R₁ is an acetyl (“Ac”), R₂ is —CONH₂, Xaa is the natural amino acid “Asp”, Yaa is the natural amino acid “His”, and Zaa is the natural amino acid “Lys”.

Cyclic Modifications

The MC5R peptide ligand is preferably a cyclic peptide formed by the bridging of Xaa to Zaa via ring closing reactions. In particular, the side chain of the Xaa residue is linked to the side chain of the Zaa residue via a linker L₁. In some embodiments, the linker L₁ is a carba, lactam, disulfide, thioether, or succinic linker. As understood by one of ordinary skill in the art, the linker is not limited to the aforementioned examples, and may depend upon the specific cyclization chemistry used to produce the cyclic peptide.

As a non-limiting example, Xaa can be linked to Zaa via an amide bond formation reaction, which may form a —(CH₂)—CO—NH—(CH₂)_(n)— bridge, where n=1, 2, 3, 4. In addition, carbon-carbon bonds, lactone, thioether, ether, disulfide and other covalent bonds can be used as a part of the ring closing reactions.

Without wishing to limit the invention to a particular theory or mechanism, the type of linker can affect the structural, chemical, and biological activity of the peptide ligand.

Ring Size Modification

Selection of Xaa and Zaa can affect the ring size of the MC5R peptide ligand. Ideally, the MC5R peptide ligand may be a 23-membered ring. For instance, as shown in FIG. 2, the MC5R peptide ligand is a 23-membered ring. In another preferred embodiment, the MC5R peptide ligand may be a 23 to 29-membered ring. As another example, if Zaa is Orn and Xaa is Glu, the MC5R peptide ligand is a 23-membered ring. As a further example, if Zaa is Lys and Xaa is Glu, the MC5R peptide ligand is a 24-membered ring.

Without wishing to limit the invention to a particular theory or mechanism, the ring size of the MC5R peptide ligand can affect the selectivity of the peptide ligand. For example, a 23-membered ring may provide a universal peptide ligand for MC1R, MC3R, MC4R, and MC5R. For a ring-size greater than 26 members, the peptide ligand may be selective for a particular melanocortin receptor, such as MC1R and MC5R.

Table 1 summarizes the modifications on the MC5R peptide ligand:

Modification Variable Variable Examples N-Terminal R₁ Acetyl, glycosylated amino acids, —CO—(CH₂)_(n)CH₃, or —CO—(CH₂)_(n)CF₃, n is 1 to 6 C-Terminal R₂ —CONH₂, —COOH, or —CH₂OH Amino Acid Xaa Asp, Glu, or Abu Yaa His, Pro, Oic, Ioc, Tic, Cpe, Che, Aic, or Acpc Zaa Lys, Orn, or Dab Amino acid Glycosylated amino acid, p-, m-, o- in the cyclic halogen or di-halogen substitution peptide of a side-chain of the amino acid Cyclic Linker L₁ carba, lactam, disulfide, thioether, or succinic linker Ring Size Xaa, Zaa 23, 24, 25, 26, 27, 28, or 29-membered ring

According to another embodiment, the present invention features a melanocortin 5 receptor (MC5R) peptide ligand according to Formula 2:

Ac-Nle⁴-c[Asp⁵-His⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Lys¹⁰]-NH₂  (PEPTIDE 9)

According to another embodiment, the present invention features a melanocortin 5 receptor (MC5R) peptide ligand according to Formula 3:

R₁-Nle⁴-c[Asp⁵-His⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Lys¹⁰]-R₂.

In one embodiment, R₁ may be an acetyl, a glycosylated amino acid, —CO—(CH₂)_(n)CH₃, or —CO—(CH₂)_(n)CF₃. Preferably, n can range from 1 to 6. In another embodiment, R₂ is an —CONH₂, —COOH, or —CH₂OH.

According to another embodiment, the present invention features a melanocortin 5 receptor (MC5R) peptide ligand according to Formula 4:

R₁-Nle⁴-c[Asp⁵-Yaa⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Lys¹⁰]-R₂.

In one embodiment, R₁ may be an acetyl, a glycosylated amino acid, —CO—(CH₂)_(n)CH₃, or —CO—(CH₂)_(n)CF₃. Preferably, n can range from 1 to 6. In another embodiment, R₂ is an —CONH₂, —COOH, or —CH₂OH. In a further embodiment, Yaa may be a natural amino acid such as His or Pro, or an unnatural amino acid such as Oic, Ioc, Tic, Cpe, Che, Aic, and Acpc.

According to further embodiment, the present invention features a melanocortin 5 receptor (MC5R) peptide ligand according to Formula 5:

R₁-Nle⁴-c[Xaa⁵-His⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Zaa¹⁰]-R₂.

In one embodiment, R₁ may be an acetyl, a glycosylated amino acid, —CO—(CH₂)_(n)CH₃, or —CO—(CH₂)_(n)CF₃. Preferably, n can range from 1 to 6. In another embodiment, R₂ is an —CONH₂, —COOH, or —CH₂OH. In some embodiments, Xaa may be a natural amino acid or an unnatural amino acid. For example, Xaa may be the natural amino acid Asp or Glu, or the unnatural amino acid Abu. In other embodiments, Zaa may be a natural amino acid such as Lys, or an unnatural amino acid such as Orn, and Dab.

As used herein, the term “about” refers to plus or minus 10% of the referenced number.

The disclosures of the following U.S. patent applications are incorporated in their entirety by reference herein: PCT/US15/35180 filed on Jun. 10, 2015.

Various modifications of the invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. Each reference cited in the present application is incorporated herein by reference in its entirety.

Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims. In some embodiments, the figures presented in this patent application are drawn to scale, including the angles, ratios of dimensions, etc. In some embodiments, the figures are representative only and the claims are not limited by the dimensions of the figures. In some embodiments, descriptions of the inventions described herein using the phrase “comprising” includes embodiments that could be described as “consisting of”, and as such the written description requirement for claiming one or more embodiments of the present invention using the phrase “consisting of” is met. 

What is claimed is:
 1. A melanocortin 5 receptor (MC5R) peptide ligand according to Formula 1: R₁-Nle⁴-c[Xaa⁵-Yaa⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Zaa¹⁰]-R₂ wherein R₁ is an acetyl, a glycosylated amino acid, or —CO—(CH₂)_(n)CH₃, wherein n ranges from 1 to 6, wherein R₂ is an —CONH₂, —COOH, or —CH₂OH, and wherein Xaa, Yaa, and Zaa are each a natural amino acid or an unnatural amino acid.
 2. The MC5R peptide ligand of claim 1, wherein the glycosylated amino acid comprises a saccharide O-linked to a natural amino acid, wherein the natural amino acid is Ser, Thr, or Tyr, wherein the saccharide is a monosaccharide, a disaccharide, or an oligosaccharide.
 3. The MC5R peptide ligand of claim 1, wherein the glycosylated amino acid comprises a saccharide N-linked to a natural amino acid, wherein the natural amino acid is Asn or Lys, wherein the saccharide is a monosaccharide, a disaccharide, or an oligosaccharide.
 4. The MC5R peptide ligand of claim 1, wherein Xaa is a natural amino acid, wherein Xaa is Asp or Glu.
 5. The MC5R peptide ligand of claim 1, wherein Xaa is an unnatural amino acid, wherein Xaa is Abu.
 6. The MC5R peptide ligand of claim 1, wherein Yaa is a natural amino acid, wherein Yaa is His or Pro.
 7. The MC5R peptide ligand of claim 1, wherein Yaa is an unnatural amino acid, wherein Yaa is selected from a group consisting of Oic, Ioc, Tic, Cpe, Che, Aic, and Acpc.
 8. The MC5R peptide ligand of claim 1, wherein Zaa is a natural amino acid, wherein Zaa is Lys.
 9. The MC5R peptide ligand of claim 1, wherein Zaa is an unnatural amino acid, wherein Zaa is Orn or Dab.
 10. The MC5R peptide ligand of claim 1, wherein Xaa is linked to Zaa via a carba, lactam, disulfide, thioether, or succinic linker.
 11. The MC5R peptide ligand of claim 1, wherein the MC5R peptide ligand is a 23 to 27-membered ring.
 12. A melanocortin 5 receptor (MC5R) peptide ligand according to Formula 2: Ac-Nle⁴-c[Asp⁵-His⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Lys¹⁰]-NH₂  (PEPTIDE 9)
 13. A melanocortin 5 receptor (MC5R) peptide ligand according to Formula 3: R₁-Nle⁴-c[Asp⁵-His⁶-(NMe)D-Nal(2′)⁷-Arg⁸-Trp⁹-(NMe)Lys¹⁰]-R₂, wherein R₁ is an acetyl, a glycosylated amino acid, or —CO—(CH₂)_(n)CH₃, wherein n ranges from 1 to 6, and wherein R₂ is an —CONH₂, —COOH, or —CH₂OH.
 14. The MC5R peptide ligand of claim 13, wherein the glycosylated amino acid comprises a saccharide O-linked to a natural amino acid, wherein the natural amino acid is Ser, Thr, or Tyr, wherein the saccharide is a monosaccharide, a disaccharide, or an oligosaccharide.
 15. The MC5R peptide ligand of claim 13, wherein the glycosylated amino acid comprises a saccharide N-linked to a natural amino acid, wherein the natural amino acid is Asn or Lys, wherein the saccharide is a monosaccharide, a disaccharide, or an oligosaccharide. 